1. Field of the Invention
The invention relates to an internal combustion engine and a method of operating an internal combustion engine.
2. Description of the Related Art
There has been known an internal combustion engine that is provided with a reformer including a reforming catalyst and that causes fuel components obtained by reforming various fuels by means of the reformer to burn in combustion chambers with a view to stabilizing combustion and reducing the amounts of HC and NOx contained in exhaust gas (Japanese Patent Application Laid-Open No. 2001-241365).
One known reformer for reforming a hydrocarbon fuel such as methanol or the like is designed to produce an intermediate product such as aldehyde or the like in a catalyst on the upstream side with respect to a flow direction of fuel and to produce hydrogen from aldehyde or the like in a catalyst on the downstream side with respect to the flow direction with a view to increasing the content of hydrogen in reformed gas (Japanese Patent Application Laid-Open No. 2000-281307). Furthermore, another known reformer is provided with a heater for heating up a reforming catalyst during a starting process of the reformer so as to produce a reformed gas that is rich in hydrogen within a short period of time (Japanese Patent Application No. 11-130405). There is also known an art wherein the air-fuel ratio in a reformer is set approximately equal to 5 as soon as the temperature of a catalyst reaches a predetermined temperature (600° C.) so as to enhance the yield of a fuel component (H2) in reformed gas (Japanese Patent Application No. 9-21362).
On the other hand, when reforming hydrocarbon fuel, suitable management of the temperature of a reforming catalyst (i.e., the temperature of a catalyst bed) is important in preventing the reforming performance from being adversely affected due to a deterioration of a catalyst, suppressing generation of by-products, and reducing the influence of heat on a region around a reformer. As a method of controlling the temperature of a reforming catalyst, there is known an art for suitably setting the temperature of the reforming catalyst by controlling the air-fuel ratio in a reformer using a correlation between the air-fuel ratio of a mixture of air and fuel supplied to the reformer and the temperature reached by the reformer (Japanese Patent Application No. 2002-179405). Documents related to this kind of art include Japanese Patent Application Laid-Open No. 4-58064, Japanese Patent Application Laid-Open No. 2002-154807, Japanese Patent Application Laid-Open No. 2000-323164, and Japanese Patent Application Laid-Open No. 11-92102.
Heretofore, as described above, the importance of suitable management of the temperature of a reforming catalyst has been accentuated in a reformer for reforming fuel. However, when an internal combustion engine equipped with a reformer is viewed as a whole, suitable management of the temperature of the reformer alone does not make it easy to produce a reformed gas for causing the internal combustion engine to operate in conformity with a required condition.